1. Field of the Invention
The present invention relates to a DC/DC converter for supplying a driving voltage to a light emitting element.
2. Description of the Related Art
For the purpose of generating higher voltage than the input voltage, step-up switching regulators are widely used in various electronic devices. Such a step-up switching regulator includes a switching element and an inductor or a transformer. With such an arrangement, the switching element is alternately turned on and off in a time division manner so as to generate back electromotive force in the inductor or the transformer, thereby boosting the input voltage, i.e., thereby outputting voltage that has been stepped up.
With an isolated DC/DC converter employing a transformer, when a switching transistor is turned on, an electrical current flows through the primary winding of the transformer, thereby storing energy in the transformer. Then, when the switching transistor is turned off, the energy thus stored in the transformer is transferred to an output capacitor in the form of a charging current via a rectifier diode, thereby generating output voltage that has been stepped up.
For example, Patent documents 1 and 2 disclose a kind of isolated DC/DC converter, i.e., a self-exciting DC/DC converter which has a configuration that does not involve an oscillator, and which has a function in which the primary winding or the secondary winding of a transformer is monitored, and on/off control is performed for the switching transistor according to the state of the primary winding or the secondary winding of the transformer thus monitored.
[Patent Document 1]
                Japanese Patent Application Laid-open No. 2004-201474[Patent Document 1]        Japanese Patent Application Laid-open No. 2005-73483        
Let us consider a case in which the aforementioned isolated DC/DC converter is used as a power supply for a flash light source for a camera. While a light emitting element such as a xenon lamp is employed as such a flash light source, there is a problem with the xenon lamp in that normal light emission by the xenon lamp requires a driving voltage higher than a predetermined voltage.
In order to solve the aforementioned problem, a control circuit of such a DC/DC converter needs to perform emission control as follows. That is to say, the control circuit monitors the driving voltage supplied to the xenon lamp. The control circuit permits light emission only in a case that the voltage thus monitored is equal to or higher than a predetermined level.